Prepare a 10-inch springform pan by wrapping it with a layer of heavy duty alum foil.
(I would grease the pan, put a round of parchment on the bottom and flour the sides) Cream together ricotta cheese, cream cheese and sugar until smooth (could use a food processor to really smooth out the ricotta).
Mix in the eggs one at a time.
Add flour one tablespoon at a time, mixing well.
Stir in the sour cream and vanilla.
(I would be sure to mix things slowly and have all ingredients up to room temperature. Don't beat any air into the mixture and be sure it's really smooth when done).
Pour mixture into pan.
Place cheesecake in a large rectangular pan filled with 2 inches of hot water.
Carefully put into preheated oven.
Bake for 90 minutes.
After 90 minutes turn oven off, but leave the cake in the oven for another 60 minutes (do not open door).
Cool on counter for at-least 60 minutes (until room temp) and then refrigerate.